Heat Exchanger for an Air Heating Device

ABSTRACT

The invention relates to a heat exchanger ( 10 ) for an air heating apparatus ( 12 ) for integration into a housing which guides air. The heat exchanger has a longitudinal axis, wherewith air can be forcibly caused to flow around the heat exchanger in a “main flow direction” which is essentially perpendicular to said longitudinal axis. According to the invention, the heat exchanger has a cross sectional geometry [sic] perpendicular to the “main flow direction” which geometry is flattened with respect to a circular cross sectional geometry ( 32, 34, 36 ).

The invention relates to a heat exchanger for an air heating apparatusfor integration into a housing which guides air. The heat exchanger hasa longitudinal axis, wherewith air can be forcibly caused to flow aroundthe heat exchanger in a “main flow direction” which is essentiallyperpendicular to said longitudinal axis.

Currently, fuel-driven supplemental heating units for vehicles(particularly trucks or utility vehicles the like) are generally housedseparately from the vehicle's inherent onboard heating and airconditioning unit. Such supplemental heating units are provided in theform of, e.g., air heating apparatuses, which are utilized as heaters toprovide supplemental heating, and/or to provide heating under stationarycircumstances (when the vehicle is parked).

For some time, attempts have been made to integrate air heating devicesinto the inherent onboard heating and air conditioning apparatus of avehicle. This would provide savings in space occupied and in componentparts (avoids redundancy). An example of such an apparatus is disclosedin DE 10211591 A1.

The quality of the functioning and the economic efficiency of the airheating apparatus, and the safety and reliability of the combination,depend substantially on the location of the apparatus integrated intothe inherent onboard heating and air conditioning system, and on theengineering design and construction characteristics of said air heatingapparatus.

It is important to fully take into account the set of problemsassociated with the integration of the air heating apparatus into thesystem of the inherent onboard heating and air conditioning system, andto provide solutions for these problems, in order to achieve asuccessful integrated system.

Some of the engineering problems concern means of minimizing theordinarily high weight of the heat exchanger body. Such heat exchangerbodies are customarily fabricated by pressure casting. The greater theweight of the heat exchanger body, the more robust the housing in whichit is mounted on the vehicle must be.

Under the design schemes according to the state of the art, air iscaused to flow around the heat exchanger in a direction which isperpendicular to the longitudinal direction (axial direction) of theheat exchanger. Such transverse flow results in high creation ofvortices and turbulent flow of the air, and thus high energy losses inthe flow (high flow pressure drop). If one seeks to address this byincreasing the space available around the heat exchanger, one will needmore installation space to accommodate the integrated heating and airconditioning system. Accordingly, it is rational to seek solutions whichimprove the flow behavior and heat transfer with regard to the heatexchanger.

It is also desirable to utilize already present components of the airheating apparatus in the solution by which said apparatus is integratedinto the inherent onboard heating and air conditioning system.Accordingly, the heat exchanger employed should have an adaptabledesign, so as to be utilizable with a variety of types and models of airheating apparatuses. The means of fabrication of the heat exchangershould be similarly adaptable.

There are two heat transfer processes—that from the heat exchanger tothe air sought to be heated, which air flows around the exterior of theheat exchanger, and that from the combustion gases to the heatexchanger. By improving the latter heat transfer, one can have greaterfreedom of design of the structure of the heat exchanger as a whole.

Another important requirement placed on the air heating apparatus isthat it be configured so as to avoid any possible penetration ofcombustion gases into the air which flows around the air heatingapparatus. Another requirement is to provide means whereby thecombustion air used for the combustion is drawn in from the spaceoutside the motor vehicle, and in particular not from the interior spaceof the vehicle. Thus it would be advantageous to provide improvements inthe arrangement of the various connecting fittings and nipples employedwith known air heating apparatuses.

The underlying problem of the present invention was to deviseappropriate solutions to solve the above-described problems at leastpartially, particularly the problems concerning flow behavior.

This underlying problem is solved by the features of the independentclaim.

Advantageous embodiments of the invention are set forth in the dependentclaims.

According to the invention, improvements are provided in the generaltype of heat exchanger in that the heat exchanger has a cross sectionalgeometry [sic] perpendicular to the “main flow direction” which geometryis flattened with respect to a circular cross sectional geometry. Such aflattened cross sectional geometry reduces flow resistance.

A flattened cross sectional geometry according to the invention may be,e.g., oval or ovaloid.

Alternatively, the cross sectional geometry may resemble that of anairfoil.

Alternatively, it may be advantageous if the cross sectional geometry isgenerally diamond-shaped.

The specifics of the cross sectional geometry can be combined withnumerous other features of the heat exchanger, of the air heatingapparatus which is to incorporate the heat exchanger, and of thefabrication processes for the heat exchanger, to give rise toadvantageous characteristics.

It may be provided that the body of the heat exchanger and the base ofthe heat exchanger are fabricated separately. This affords flexibilitywith regard to the various possible structures and configurations, andthe various possible fabrication methods. If the heat exchanger base isfabricated separately from the heat exchanger core, variants infabrication methods and steps for the heat exchanger core may beintroduced. The overall weight of the heat exchanger can be reduced bythe appropriate choice of fabrication methods.

For similar reasons, it may be advantageous to fabricate the heatexchanger head separately.

In particular, such a heat exchanger head may be already available;wherewith separate fabrication is a beneficial choice. Depending on thegeometric form of the burner head or of the burner unit, it may even bepossible to completely eliminate a heat exchanger head.

According to another preferred embodiment of the invention, the heatexchanger body has a heat exchanger core and heat transfer surfaces, andthe heat exchanger core and the component parts which provide the heattransfer surfaces, are at least partially separately fabricated. Thesepossible separate fabrication processes are advantageous as means ofweight reduction and means of providing increased variability withregard to the configuration of component parts and with regard tofabrication methods.

In this connection it is particularly useful if the component partswhich provide the heat transfer surfaces are applied to the heatexchanger core by press-forming or by a shrink-forming method. In orderto join the heat exchanger head and the heat exchanger base to the heatexchanger core with gas-tight joints, preferably welding, brazing,adhesive bonding, and/or screwing (or screw fastening) are employed.There may be, e.g., heat transfer surfaces [sic] of the heat exchangerwhich generally have a disc-like or flange-like shape, wherewithpress-forming or shrink-forming may be advantageous for fixing them tothe heat exchanger core. In this way, one has additional opportunitiesfor variability of the fabrication methods.

It is possible to fabricate the heat exchanger core by pressure casting.In general, such cast parts are somewhat heavy; however, cost savingsare achieved.

It is possible to provide the heat exchanger core with an interiorprofile. This is a means of increasing the interior heat transfersurface area of the heat exchanger, and of decreasing the overallinstallation space required.

The heat exchanger core may be manufactured by extrusion. Extrusiongenerally allows for thinner walls in the heat exchanger compared to acore fabricated by pressure casting, in particular since extrusion doesnot require the configuration to include a mold removal incline;accordingly, reductions in overall weight can be achieved, as well asthinner features (vanes etc.) in the interior profile, and therebyincreased heat transfer surface area of the interior surfaces. Anextrusion process makes it possible to incorporate geometric featureswhich facilitate attachment of the heat exchanger head, burner, heatexchanger base, etc., e.g. in the form of holes in the core which may bethreaded.

The heat exchanger body may have a plurality of rods on its exteriorsurface, which rods provide heat transfer surface. This configurationcan contribute a very large surface area for heat transfer to the airwhich is to be heated.

It may be advantageous for the heat exchanger body to have a heatexchanger core, and for the above-described plurality of rods to beapplied to said core at least partially by means of a separate componentpart (or parts).

The heat exchanger body may have a heat exchanger core wherewith atleast part of (some of) the plurality of rods have a unit constructionwith the heat exchanger core. The provision of the rods on one or moreseparate component parts, on the one hand, and direct fixing of the rodsto the core (in a unit construction or the like), on the other hand,each has its own advantages; e.g. the use of separate component partsprovides design flexibility, whereas direct fixing (e.g. unitconstruction) allows a simple fabrication method.

The heat exchanger body may have a plurality of undular ribs on itsexterior surface, which ribs contribute heat transfer surface area.

In this connection, it is possible that the heat exchanger body has aheat exchanger core wherewith the plurality of undular ribs are appliedto the heat exchanger core via a separate component part or asindividual separate parts.

In a configuration in which the heat exchanger body has a heat exchangercore, the plurality of undular ribs may be at least partly (e.g. atleast some of them may be) fabricated in a unit construction with theheat exchanger core. It is advantageous if the means of fastening suchheat transfer surfaces are not screw means or the like

In connection with an air heating apparatus for integration into an airguiding housing, which heating apparatus has a heat exchanger with aheat exchanger body, the air heating apparatus may be provided withflow-guiding elements wherewith, when combustion is carried out in acombustion space which is at least partly disposed in the interior ofthe heat exchanger, hot gases which are generated are deflected towardthe interior side of the heat exchanger body. In this way, the hot gasesproduced in the combustion can be more efficiently distributed over theinterior side of the heat exchanger.

In this connection it is advantageous if the flow guiding elements arein the form of a helical vane, systems of vanes or the like (which mayemploy undular geometries or the like), baffle plates, and/or perforatedtubes. These and numerous other possibilities improve overall heattransfer.

In the case of an air heating apparatus for integration into an airguiding housing, which apparatus has a heat exchanger, it may beadvantageous if the apparatus has a flange plate which provides a sealof the exhaust gas withdrawal means, by means of sealing elementsbetween a mounting location for the air heating apparatus and the flangeplate, and between the air heating apparatus and the flange plate, whichseal at least prevents penetration of exhaust gases into the interiorspace of the vehicle. Such a flange plate provides means of minimizingthe path of the exhaust gases to the external air, and in so doing makesit less likely that penetration will occur.

In this connection it is further useful that the flange plate providesseal means between the combustion air feed passage and the interiorspace of the vehicle. This provides assurance that the combustion airwill be drawn from outside the vehicle.

It is also advantageous if the flange plate has a pass-through openingfor fuel supply. In this way, all fittings and nipples through whichgases and liquids are passed are disposed in the region of the flangeplate, which is advantageous for integrating the air heating apparatusinto the entire system design.

It is an underlying concept of the invention that an air heatingapparatus can be integrated into an onboard heating and air conditioningsystem of a vehicle (particularly a truck or utility vehicle) in aneconomical and functionally advantageous manner. In implementation ofthis concept, a heat exchanger has been devised according to theinvention which has high variability and adaptability, and hasadvantageous weight, flow, and heat transfer characteristics.

The invention will now be explained further based on particularlypreferred exemplary embodiments, with reference to the accompanyingdrawings.

FIG. 1 is a perspective view of an air heating apparatus;

FIG. 2 is a perspective view of an air heating apparatus sans heatexchanger;

FIG. 3 is a perspective view of an air heating apparatus sans heatexchanger, disassembled into two subassemblies, namely the burner headand the burner unit;

FIG. 4 is a perspective view of a heat exchanger;

FIG. 5 is a perspective view of individual components of a heatexchanger;

FIG. 6 is a perspective view of an air heating apparatus with housingattachment means applied;

FIG. 7 is a cross sectional view of a heat exchanger core having an ovalcross section;

FIG. 8 is a cross sectional view of a heat exchanger core having agenerally airfoil-shaped (lobe-shaped) cross section;

FIG. 9 is a cross sectional view of a heat exchanger core having agenerally diamond-shaped cross section;

FIG. 10 is a perspective view of a heat exchanger, showing separately anindividual heat transfer component;

FIG. 11 is a perspective view of a variant embodiment of a heatexchanger;

FIG. 12 is a perspective view of another variant embodiment of a heatexchanger;

FIG. 13 is a perspective view of yet another variant embodiment of aheat exchanger;

FIG. 14 is a perspective view of a plurality of heat exchanger bodymodules which are mutually identical;

FIG. 15 is a perspective cutaway view of a heat exchanger;

FIG. 16 is a perspective view of a combustion tube;

FIG. 17 is a perspective view of a variant embodiment of a combustiontube;

FIG. 18 is a perspective view of another variant embodiment of acombustion tube; and

FIG. 19 is a perspective view of a connecting region of an air heatingapparatus with a flange plate.

In the description of the drawings which follows hereinbelow, like orsimilar components have been assigned like reference numerals.

FIG. 1 is a perspective view of an air heating apparatus 12, comprisedof a heat exchanger 10 mounted on a burner unit 60, and furthercomprised of a burner head 62. The burner head 62 contains a blowermotor 64 and a control device 66 which comprise the essential componentsof a combustion air blower unit 68. The burner head 62 also has a nipple56 for supply of combustion air. The burner unit 60 has a fuel supplyline 58 and a nipple 54 for withdrawal of exhaust gas The exhaust gasnipple 54 bears a flange plate 48 which has openings for the fuel supplyline 58 and the combustion air supply line 56. The function of theflange plate 48 will be described in more detail infra with reference toFIG. 19. The heat exchanger 10 mounted on the burner unit 60 has a ribstructure on its exterior perimeter, so as to increase the surface areafor heat transfer to the air flowing over the heat exchanger 10. The airheating apparatus 12 preferably is oriented with respect to the airstream of the air which is to be heated, such that the latter approachesand leaves in a direction perpendicular to the axis of the heatexchanger 10, as said air flows around and past said heat exchanger 10.

FIG. 2 is a perspective view of an air heating apparatus 12, sans heatexchanger. Here the burner head 62 and burner unit 60 are more clearlyvisible. The burner unit 60 comprises a combustion tube 70 in which hotgases are produced with flame formation; heat from the hot gases istransferred to the heat exchanger 10 (which is not shown in FIG. 2). Toenable the hot gases to reach the heat exchanger, a plurality of holes72 are provided in the wall of the combustion tube 70.

FIG. 3 is a perspective view of an air heating apparatus 12 sans heatexchanger, disassembled into two subassemblies, namely the burner headand the burner unit. This Figure shows clearly how the burner head 62[lit., “60”] is connected to the burner unit 60 via a flange joint (74,76). Further, it is seen clearly in this Figure that the flange plate 48is fixedly joined to the exhaust gas nipple 54, whereas a pass-throughopening for the combustion air line 56 is provided in the flange plate.

FIG. 4 is a perspective view of a heat exchanger 10. The ribbedstructure can be seen, which provides heat transfer surfaces 22.

FIG. 5 is a perspective view of individual components of a heatexchanger 10. It is seen that the heat exchanger 10 has a plurality ofcomponent parts. It is comprised of a heat exchanger core 20, components24 with heat transfer surfaces 22, a heat exchanger base 16, and a heatexchanger head 18. Depending on the configuration of the burner head 62and/or the burner unit 60, the heat exchanger head 18 may beunnecessary. Inside the heat exchanger core 20 an interior profile 30 isprovided which facilitates heat transfer from the hot gases generated inthe combustion tube 70 to the heat exchanger 10. The heat exchanger head18 and heat exchanger base 16 may be fabricated by various techniques,e.g. deep drawing, pressure molding, or machining. The individualcomponent parts can then be joined by various joining techniques, e.g.welding, brazing, adhesive bonding, and/or screwing or screw fastening.Because combustion gases are present inside the heat exchanger 10, it isimportant that gas-tight joints be provided between the heat exchangerhead 18, heat exchanger core 20, and heat exchanger base 16. In thecontext of the present disclosure, the heat exchanger core and thecomponents 24 with heat transfer surfaces 22 are commonly designatedwith the reference numeral 14.

FIG. 6 is a perspective view of an air heating apparatus 12 with housingattachment means 74 [sic] applied, to facilitate attachment of the airheating apparatus to a surrounding housing. The said housing attachmentmeans 74 are attached to the air heating apparatus 12 via the heatexchanger head 18 and the heat exchanger base 16.

FIG. 7 is a cross sectional view of a heat exchanger core having an ovalcross section. The heat exchanger core 20 has an interior profile 30.The finer the configuration of this interior profile 30, the greater thesurface available for heat transfer from the hot gases to the heatexchanger 10. A heat exchanger core 20 of the type illustrated can befabricated by means of, e.g., an extrusion process. Such a processallows for thin walls, with the advantage of low weight and theprovision of a large heat transfer surface area. The heat exchanger core20 has means of fastening, e.g. openings 76 [sic], to facilitateattachment of the other components. The oval cross sectional geometry(32) of the heat exchanger 20 can improve flow characteristics for theair which is to be heated, which air flows around and past the heatexchanger 20. Because the heat exchanger base 16 is fabricatedseparately from the heat exchanger core 20, the fabrication of the core20 is made easier.

FIG. 8 is a cross sectional view of a heat exchanger core having agenerally airfoil-shaped (lobe-shaped) cross section.

FIG. 9 is a cross sectional view of a heat exchanger core having agenerally diamond-shaped cross section. The cross sectional geometriesillustrated (airfoil-shaped 34 and diamond-shaped 30) are merelyexamples of numerous possible shapes which are favorable for the flowaround the exterior of the heat exchanger 20.

FIG. 10 is a perspective view of heat exchanger 10, showing separatelyan individual heat transfer component 24. Each component 24 isfabricated separately from the heat exchanger core 20. The components 24which are shown mounted on the heat exchanger core 20 are fixed to saidcore by sliding them over the core and then applying, e.g.,press-forming or a shrink-forming technique; said components 24 areattached individually or in groups or subassemblies.

FIG. 11 is a perspective view of a variant embodiment of a heatexchanger 10 which has a very large surface area for transferring heatto the air flowing around it. This large surface area is achieved by aheat transfer surface 22 comprised of a plurality of rods 26.

FIG. 12 is a perspective view of another variant embodiment of a heatexchanger, having an even larger heat transfer surface area, provided bya very large number of rods 26 which afford the heat transfer surface22. The interior profile 30 may also be seen, in the interior of theheat exchanger. In the embodiment illustrated, some elements of thisinterior profile comprise extensions of features on the exteriorprofile, namely the exterior rods 26; or correspond to extensions ofrows of such exterior rods. The rods 26 of the embodiments illustratedin FIGS. 11 and 12 may be applied to the exterior surface of the heatexchanger as separate components therefrom, or may be formed, e.g., froman extruded profile by press-forming or machining.

FIG. 13 is a perspective view of yet another variant embodiment of aheat exchanger 10. The components 28 which provide the heat transfersurface 22 of the heat exchanger are undular ribs, which promote heattransfer.

FIG. 14 is a perspective view of a plurality of heat exchanger bodymodules 38 which are mutually identical. This embodiment is particularlyinteresting in that it is amenable to fabrication by pressure casting,which may be desired in some cases (in comparison to extrusion,mentioned above). A drawback of pressure casting is that inherently thethicknesses of walls may be greater as a result of mold removal angles(mold removal inclines). In the exemplary embodiment illustrated, theaxial length of each of the heat exchanger body modules 38 is short,wherewith the said thicknesses can be kept small because the moldremoval inclines are correspondingly short.

FIG. 15 is a perspective cutaway view of a heat exchanger 10. Thisembodiment enables another casting process in which mold removalinclines are kept short. The heat exchanger 10 is produced by pressuremolding and has two heat exchanger cores which are removed from the moldin two opposite removal directions (40, 42); with this arrangement, thethicknesses of walls can be kept small.

FIGS. 16, 17, and 18 are perspective views of three different combustiontubes 70. In order to provide for good and uniform transfer of heat tothe interior surface of the heat exchanger from the hot gases generatedin the combustion, with maximally efficient distribution [sic], it isadvantageous to employ flow guiding means to deflect the hot gasesdisposed inside the heat exchanger 10 against the interior profile(vanes or the like) 30 and against the interior wall. In FIG. 17, theflow guiding element 44 has a helical configuration. Alternatively, theflow guiding elements may be in the form of vanes or the like (and mayemploy undular geometries or the like), baffle plates, and perforatedtubes; as shown in FIG. 18, such a perforated tube may have a pluralityof openings 46 in addition to the pattern of openings 72.

FIG. 19 is a perspective view of a connecting region of an air heatingapparatus with a flange plate 48. The flange plate 48 serves formounting of the air heating apparatus 12 [lit., “10”] to the body of avehicle or to a housing or other component which in turn is mounted tothe vehicle body. In order to provide for venting of the exhaust gasesto the surroundings and intake of combustion air from the surroundings,the flange plate 48 is sealingly connected to the air heating apparatus12 and [sic] to the mounting location (e.g. the vehicle body). Thesealing may employ sealing rings, for example.

The features of the invention disclosed in the preceding description,the drawings, and the claims may be essential elements of the inventionindividually or in any combination.

List of Reference Numerals:

-   10 heat exchanger.-   12 air heating apparatus.-   14 heat exchanger body.-   16 heat exchanger base.-   18 heat exchanger head.-   20 heat exchanger core.-   22 heat transfer surface.-   24 component parts having heat transfer surfaces (disc-shaped).-   26 component parts having heat transfer surfaces (rod-shaped).-   28 component parts having heat transfer surfaces (undular ribs).-   30 interior profile [(FIGS. 5, 7); generally diamond-shaped external    profile (FIG. 9)].-   32 oval (or ovaloid) cross sectional geometry.-   34 airfoil-shaped (lobe-shaped) cross sectional geometry.-   36 generally diamond-shaped [lit., “shaft-shaped”] cross sectional    geometry.-   38 heat exchanger body module.-   40 mold removal direction.-   42 mold removal direction.-   44 screw thread.-   46 hole in perforated tube.-   48 flange plate.-   54 exhaust gas removal [nipple].-   56 combustion air supply line.-   58 fuel supply line.-   60 burner unit.-   62 burner head.    -   [(End of reference numeral list supplied for translation.)]    -   [(Note that reference numeral 74 has a different meaning in FIG.        6 than in FIG. 3; and that reference numeral 76 has a different        meaning in FIG. 7 than in FIG. 3.)]

1. A heat exchanger (10) for an air heating apparatus (12) forintegration into an air-guiding housing, which heat exchanger has alongitudinal axis, wherewith air can be forcibly caused to flow aroundthe heat exchanger in a “main flow direction” which is essentiallyperpendicular to said longitudinal axis; characterized in that the heatexchanger has a cross sectional geometry [in a cross sectional plane]perpendicular to the “main flow direction” which geometry is flattenedwith respect to a circular cross sectional geometry (32, 34, 36).
 2. Aheat exchanger (10) according to claim 1; characterized in that thecross sectional geometry (32) is oval or ovaloid.
 3. A heat exchanger(10) according to claim 1; characterized in that the cross sectionalgeometry (34) is similar to the cross sectional shape of an airfoil. 4.A heat exchanger (10) according to claim 1; characterized in that thecross sectional geometry (36) resembles a diamond shape.